Hot deformation behavior and processing map of Ti-6Al-6V-2Sn titanium alloy

Abstract

Deformation behavior of Ti-6Al-6V-2Sn alloy possessing an equiaxed α-β preform microstructure was theoretically simulated at a temperature of 800 °C–920 °C and at a strain rate of 0.01–10 s−1 for the purpose of analyzing its processing window and microstructure evolution during hot processing. As temperature increased, flow stress decreased when alloy samples were deformed at a fixed strain rate. Softening behavior can be observed at lower temperatures at all strain rates, which can possibly be explained by the dynamic recrystallization (DRX) of the lamellar α-phase. Alloy microstructure did not change significantly during deformations when the temperature is lower than 830 °C. Thus, the microstructure evolution of Ti-6Al-6V-2Sn alloy could only be quantitatively described under such conditions. For deformations occurring in the range of 830 °C–860 °C, α-polymorph formed spherical clusters, whereas β-polymorph underwent DRX. With regard to temperature above 860 °C, content of the initially major α-phase declined rapidly. Meanwhile, content of the secondary acicular martensite α′-phase rose up, and grains of the β-polymorph became larger. At strain rate equals to 0.1 s−1, flow stress peak was not able to be observed at the initial stage. When it finally became detectible, the value of the flow stress peak first went up and then gradually fell down. Such behavior was attributed to the formation of three different phases at a certain condition (α-Ti, β-Ti and α″-Ti). Optimum hot deformation conditions of Ti-6Al-6V-2Sn determined from the processing map were in the temperature range of 887 °C–920 °C and at 0.01–0.75 s−1 strain rates.